The present invention relates to a heavy-duty power transmission V-belt.
In conventionally well known heavy-duty power transmission V-belts, a large number of blocks are fixed on a tension member by using convex and concave engagement structures of the blocks and the tension member as is disclosed in Japanese Laid-Open Utility Model Publication Nos. 1-55344 and 6-69490 and Japanese Laid-Open Patent Publication No. 5-272595, and such heavy-duty power transmission V-belts are utilized in the field of, for example, stepless transmission. In such a conventional V-belt, the blocks are fixed on the tension member not through adhesion but through physical engagement in order to secure flexibility of the belt. The belt includes a pair of right and left tension members 1 arranged in a widthwise direction of the belt, for example, as is shown in FIG. 2. On the upper face and the lower face of each tension member 1, upper concave parts 2 and lower concave parts 3 are respectively correspondingly provided as a larger number of engaged parts arranged in the lengthwise direction of the belt. On the other hand, on the side faces of each block 7 in the widthwise direction of the belt, a pair of right and left fitting parts 8 each in the shape of a notch groove are respectively formed so as to catch the tension members 1 therein. Each of the fitting parts 8 is provided with upper convex parts 9 as upper engaging parts formed on its upper face and lower convex parts 10 as lower engaging parts formed on its lower face. By pressing the tension members 1 so as to be fit in the right and left fitting parts 8 of the respective blocks 7, the respective blocks 7 are fixedly engaged with the tension members 1.
Such a heavy-duty power transmission block V-belt in which a large number of blocks 7 are compressedly fixed on the pair of tension members 1, however, has the following problems: First, an innermost structure between the innermost portion of the fitting part 8 of the block 7 and the end of the tension member 1 closer to the center in the widthwise direction of the belt to be fit in the fitting part 8 will now be described. In order to prevent stress from being collected on the block 7, the upper and lower corners of the innermost face of the fitting part 8 and the upper and lower corners of the innermost end of the tension member 1 are inclined as is shown in FIG. 11. Furthermore, in order to reduce the stress collection, innermost angles, that is, the angles of the upper and lower corners thereof are generally set to approximately 45 degrees against a vertical plane.
However, when the belt is used for a long period of time, imbalanced abrasion is caused in the engagement part between the tension member 1 and the block 7, specifically, in an outside portion of the upper face of the tension member 1 and an inside portion of the lower face of the tension member 1 as is shown with virtual lines in FIG. 11. Due to the dimensional change derived from the imbalanced abrasion, load shares of tension cords 1b within a form holding layer 1a of the tension member 1 become ununiform, namely, the load increases toward the outside of the fitting part 8 in the tension cords 1 arranged in the widthwise direction of the tension member 1. Accordingly, a load applied to one tension cord 1b is increased so as to accelerate the fatigue of the tension cord. As a result, time until breakage of the tension cord 1b is shortened, resulting in lowering the durability of the belt.
Furthermore, in order to reduce noise of the belt, the block belt is provided with a projecting margin formed by appropriately projecting a side face of the tension member 1, that is, a rubber belt, from the side face of the block 7 (See Japanese Laid-Open Utility Model Publication No. 6-69490 and Japanese Laid-Open Patent Publication No. 5-272595). Owing to this projecting margin, the side faces of both the tension member 1 and the block 7 can come in contact with the groove face of a pulley, so that the mechanical shock caused when the block 7 meets the pulley can be absorbed and the noise can be reduced. However, when the imbalanced abrasion is caused in the tension member 1, the side face of the tension member 1 recesses from the side face of the block 7 and the projecting margin becomes minus, resulting in increasing the noise of the belt.
Assuming that one of the tension members 1 is one V-belt, the imbalanced abrasion seems to be caused by the moment M derived from directional imbalance between a force F applied to the tension member 1 by the groove face of a pulley and a force applied by the innermost face of the fitting part 8 of the block 7. The moment M is caused so as to push upward the outside portion of the tension member 1 closer to the groove face of the pulley and push downward the opposite portion thereof closer to the innermost face of the fitting part 8.
On the other hand, the blocks 7 are fixed on the tension members 1 through convex and concave engagement in the block belt. However, the engagement between the tension members 1 and the blocks 7 can be loosen, while driving the belt, due to permanent set in fatigue and abrasion of the engaged parts of the tension members 1 and abrasion of the engaging parts of the blocks 7, and the blocks 7 become rickety. As a result, the fatigue of the tension cords 1b of the tension member 1 is accelerated. Alternatively, the noise of the belt is increased due to vibration of the blocks 7.
In order to overcome these problems, in addition to the projecting margin provided to the block belt, by setting an engagement thickness of the tension member 1 to be larger than an engagement gap of the block 7, the belt is provided with a fitting margin for compressedly fitting the tension members 1 in the fitting parts 8 of the blocks 7 (see Japanese Laid-Open Utility Model Publication No. 1-155344). Thus, time until the blocks 7 and the tension members 1 start to become rickety can be postponed. However, when the fitting margin and the projecting margin are larger, there arises another problem of increase of heat generation in the belt.
Furthermore, the durability of the belt can be improved by improving accuracy in the dimensions, such as a thickness, of the tension members 1 and the blocks 7 and by setting the projecting margin and the fitting margin at an optimal level. However, when the fitting margin becomes loose to a given extent, the imbalanced abrasion is caused in the tension member 1, and hence, there is a limit in the improvement of the durability of the belt. When the belt is used under severe conditions (such as a small pulley diameter, large torque and a high temperature), the durability of the belt cannot be improved by the aforementioned means, and it is necessary to provide means for suppressing the imbalanced abrasion.
An object of the invention is improving the innermost structure of a belt between the innermost portion of the fitting part of each block and the innermost end of the tension member fit in the fitting part, improving the durability of the belt by suppressing imbalanced abrasion of the tension member, and reducing noise of the belt even in use for a long period of time by setting the projecting margin and the fitting margin large with suppressing heat generation in the belt.